A code editor is a program that you use to read, create, and edit code.
In the past I recommended that students use one of:
However, GitHub announced that they are no longer going to support Atom beyond December 15, 2022. So, I would explicitly not recommend it now. Atom has been my editor of choice for the past few yeras, so I'm sad to see it go.
Before Atom, Sublime Text was my editor of choice. Sublime was the earliest of the modern, lightweight code editors, so it has had a lot of time to mature and remains an excellent option. The main downside for Sublime IMO is that it is not free (which was acceptable early on, but is harder to justify when there are decent free options available).
I have recently switched from Atom to VS Code. VS Code is a solid code editor, and dances farther past the lines around the definition of a code editor. There's a large community of developers around VS Code that contribute plugins for code formatting, git initegration, and many other features.
Between Sublime and VS Code you can't really go wrong.